Transcript More studies on the stau - ep

Status report from the
LEPSUSYwg: “The stau excess”
F Cerutti, G.Ganis, F.Holldorfer, K.Jakobs and
M.Maggi



The facts:

First look to the excess

Studies going on …
Perspectives for 2000 run

Signal hypothesis

Fluctuation hypothesis

Possible strategy
Conclusions ?!?
13 April 2000
F.Cerutti
1
The facts: combined excess

stau ADLO 189-202 GeV combined

Exchanged matrixes in the Mstau-Mchi
plane : Cand, Bkg, Eff
2
The facts: excess probability

Estimator used to quantify the excess
CLNoExcess  P(O  O obs )
L( si  bi )
obs
obs
O  Exp, Ecm ni  wi ; wi 
L(bi )
3
The facts: excess probability
4
The facts: excess probability

E fraction of point with CLexcess<2%

Gedanken experiments (bkg only)

Pexcess = N(E>Edata)/Ntot =10-3 (6.8% A)
5
Mstau from xs

Find the stau mass comparing stR vs
data excess (Mc<30):

MtR = (86.7 ± 1.4) GeV (Mc~15-35)
6
The reference point

Take as “reference point”
Mt=85 GeV Mc=20 GeV:

Cand = 226

Bkg = 179.5

P(Bkg,NNcand) = 5 x 10-4
A
D
L
O
Tot
Can
50
34
70
72
226
Bkg
36.8
28.2
55.8
58.7
179.5
5.8 5.8
14.2 8.4 13.38.5 46.515.1
40%
30%
25%
55%
-
/Vb 6.6%
5.6%
3.3%
7.2%
-
Diff 13.27.1

7
Compatibility with signal in the
reference point : ALEPH only
8
Bkg composit. and systematics

Background composition in 85-20:
Proc
4f
A
D
L
O
92.4%
75.1%
78.3%
86.7%
ll
6.3%
11.3%
11.5%
5.7%
qq
-
-
7.4%
-
tt()
1.3%
12.1%
1.7%
4.0%
ll()
-
1.5%
1.1%
0.6%
other
-
-
-
3.0%

Systematics on bkg: ~2-4% dominated
by MC statistics

If we add 4% to bkg in 85-20:
P(Bkg,NNcand) = 3 x 10-3

Gedanken experiment full plane with
bkg sys (+1s):
Pexcess=N(E>Edata)/Ntot=1.2%
9
Comparison Data vs Bkg

Decided to exchange more info within
ADLO to allow additional checks

For each event (Data, MC Bkg and MC
signal) exchange:
Pt1 Pt2 Pmiss Weight(bkg) Bin-position, ...

For the 85-20 point check variables
[Bkg vs Data] ADL(189-202)O(189)
DT=184
MC=146.
Excess = 38±14
(2.7 s)
10
Comparison Data vs Bkg

Emax

Emin

Mtt

Ptmiss

Acollinearity

Emax vs Emin

Mt1 vs Mt2

Tau ID1 vs Tau ID2
11
ALEPH: H+ vs stau (B.Fabbro)

H+ vs stau Large-dM (L-dM.OR.S-dM):
189
can bkg
can
bkg
20 15.5
20
15.5
192-202 36
(M=85)


35.5
38%
30(46) 21.7(34.2)
39%
The two analyses are NOT incompatible

cand=16 bkg=17 dif=-1±4
H+ only

cand=10 bkg=4
stau only

cand=20 bkg=18 dif=2±4
dif=6±3
H+.AND.stau
Warning: 9 events (5 large-dm) selected
by stau and NOT by H+ have a NOT
identified energetic lepton -> to be
checked !
12
Perspective for y2k run

Patrick performance for LEP y2k
13
Perspective for y2k run

Studied 18 configurations:

1 22 weeks at 192 GeV

2
“
196 GeV

3
“
198 GeV

4
“
200 GeV

5
“
202 GeV

6
“
203 GeV

7
“
204 GeV

8
“
204.6 GeV

9 “

10 “

11 22 w
205.2 GeV
206 GeV
206.8 GeV
14
Perspective for y2k run


12 22 w MiniRamp 1-step 4-bun.

13 22 w MR + 24 w extens. MR

14 22 w + 24 w extens. 200 GeV

15 Status at LEPC in July MR

16 MR up to LEPC+200 GeV 22+24

17 MR up to LEPC+200 GeV 22+2

18 Status before 2000 run
Results for signal hypothesis in the
given for three stau masses: 85, 87 and
89 GeV (mild dependence from Mc=20
GeV)
15
Mt=87 GeV
16
Mt=85 GeV
Mt=89 GeV
17
Significance for Mstau =
89-85 GeV

1 22 weeks at 192 GeV
3.1-3.9 sigma

2
“
196 GeV
3.4-4.3 sigma

3
“
198 GeV
3.5-4.3 sigma

4
“
200 GeV
3.6-4.3 sigma

5
“
202 GeV
3.6-4.2 sigma

6
“
203 GeV
3.6-4.1 sigma

7
“
204 GeV
3.6-4.0 sigma

8
“
204.6 GeV
3.5-4.0 sigma

9 “
205.2 GeV
3.5-3.9 sigma

10 “
206 GeV
3.1-3.3 sigma

11 22 w
206.8 GeV
3.1-3.3 sigma

12 22 w MiniRamp 1-step
3.4-3.8 sigma

13 22+24 w MR
3.8-4.5 sigma

14 22+24 w 200 GeV
4.1-5.3 sigma

15 Status at LEPC in July mr
3.2-3.5 sigma

16 MR up to LEPC+200 GeV (22+24) 4.1-5.2 sigma

17 MR up to LEPC+200 GeV (22+2) 3.5-4.2 sigma

18 Status before 2000 run
2.9
sigma
18
Perspective for y2k run:
No signal hypothesis

Question:
can we exclude at 95% CL 85<Mt<89
with next year data alone ?

Answer:
YES but for configurations 10, 11,
15 and 17(89 GeV only) !

10 Ecm=103

11 Elep=103.6

15 Status at LEPC with MR

17 MR up LEPC then 198 GeV
19
Conclusions ?!?

The facts:





An excess in the ADLO combined LEP
data has been found
This excess corresponds to a
probability ~10-3 without any bkg
systematics
With the bkg systematics included it
goes up to ~0.5-1% (not a discovery !)
To be better understood background
systematics (A lepton ID)
Y2K run: signal hypothesis:

4-5 sigma significance still reachable
if emphasis to L is given and 6
months extension is obtained
20
Conclusions ?!?



At the July LEPC significance could
increase from the actual 2.9 to [3.33.5] sigma (assuming a successful
MR run)
Significance [3.8-5] sigma could still
be reached if, after LEPC, run is
optimized for L (run at ~200 GeV)
.AND. the 6 months extension is
given
Y2K run: no signal hypothesis:

A [85-89] GeV stau mass can be
excluded at 95% CL by next year run
alone in all the run configurations but
the run at the highest energy (103
GeV)
21
Y2K optimal stau strategy ?!?


Run with MR up to LEPC ~ 120pb-1 than:

Higgs exclusion (Kinematic limit ?)

Stau excess significance (+ or - ?)
If + indication for stau AND - for H
(and c+): switch from MR to optimal
stau run (large L at Elep~200)

Final decision on 6 months extension
should be taken later (and/or as soon as
the 4 sigma are reached): August-
September ?

Ongoing work:

Careful review of bkg systematics

Provide signal files and fit for MstauMchi (xs plus shapes)

Schedule regular meetings during
y2k run
22